1. Field of the Invention
The invention relates to a reference setting tool used to measure the shape of driven teeth (spline teeth) of a side face spline formed on a vehicle hub unit, a shape measuring device using the reference setting tool, and a shape measuring method using the reference setting tool.
2. Description of Related Art
A hub unit is used to support a wheel of an automobile such that the wheel is rotatable with respect to a suspension. There is a known hub unit in which a side face spline having driven teeth (spline teeth) to be meshed with drive teeth, formed on an outer ring of a constant velocity joint, is formed on an axially inner end face (an end face on the inner side in the vehicle lateral direction) of a hub wheel to which a drive wheel is fitted (refer to, for example, Published Japanese Translation of PCT Application No, 2008-536737 (JP 2008-536737 A) and Japanese Patent Application Publication No. 2008-174178 (JP 2008-174178 A)). In the hub unit, torque of a drive shaft of an automobile is transmitted from the constant velocity joint to the hub wheel via the driven teeth.
The driven teeth of the above-described side face spline need to satisfy predetermined accuracy requirements for various dimensions such as a tooth flank size, an arrangement pitch and a coaxiality with respect to the rotation center, in order to appropriately mesh the driven teeth with the drive teeth of the constant velocity joint. Therefore, after a hub unit is manufactured, an inspection process is carried out. In the inspection process, for example, a three-dimensional measuring device is used to measure various dimensions of the driven teeth, and whether predetermined accuracies are achieved is checked.
The shape of the driven teeth of the side face spline is usually designed using a pitch surface when the driven teeth are in mesh with the drive teeth of the constant velocity joint, as a reference surface (e.g. an imaginary plane indicated by the long dashed double-short dashed line α in FIG. 2; hereinafter, also referred to as “design reference surface”). However, because the design reference surface is just an imaginary plane, the design reference surface cannot be used to measure the shape of the driven teeth of an actual product in the inspection process. Therefore, in related art, various dimensions of spline teeth are measured using a worked surface, such as a flange surface and a wheel fitting surface of a hub wheel, as a temporary reference surface. However, this increases measurement errors, which makes it difficult to stably carry out accurate dimension measurement.